Radio communications based upon frequency modulation of an information signal of interest are well known in the art. To date, most such radios have been analog based. Nevertheless some progress has been made in digitizing at least a portion of the reception, demodulation and/or audio processing functions of such a radio.
In order to facilitate such digital processing, the received FM signal must, at some point, be digitized through an appropriate sampling process. This signal may then be further processed to provide a digital signal suitable for demodulation and subsequent processing.
Well accepted sampling theory teaches that the signal to be sampled (see FIG. 1) should be sampled at frequency at least twice the bandwidth (+/-fFM in FIG. 1) of the original signal. Therefore, if we presume reception by the FM radio of an FM signal consigned to a plus/minus 12.5 kHz channel, an acceptable sampling rate of the FM signal (presuming zero IF) (f.sub.S in FIG. 2) must be 25 kHz or higher. If this criterion is not met, the frequency images can overlap one another (as depicted in FIG. 3), thereby giving rise to aliasing. According to traditional sampling theory, once a signal has been subjected to aliasing, it is theoretically impossible to reconstruct the original analog signal.
Because of this limitation, an FM radio that makes use of a digital signal processing platform must devote a significant amount of its resources towards processing of a significant number of samples that are representative of the original analog information signal.